Portsmouth have confirmed that a deal to sell Pearce is in place, and Warnock says he wants “decisive progress” in the transfer market next month.
Leeds finished 14th in the Championship after Saturday’s 2-1 defeat to Leicester City.
Pearce, who joined the south coast on a £500,000 transfer from Bournemouth last summer, will cost Leeds a similar six-figure sum.
Portsmouth have entered administration and failed to stave off relegation from the Championship, and Pearce was left out of their final match at Nottingham Forest.
Warnock planned to announce his first summer signing this week and United will release their retained list on Wednesday, confirming which existing players are part of his plans.
He said: “I go away at the end of May for a couple of weeks and in my own mind I want to have at least three or four lads lined up by that stage.
“You’ll see my intentions on Wednesday when we put out the retained list, but the sooner the better with new players after that.
“As a manager you need to know what nine or 10 of your players are going to do. As I’ve said before, it’s the toss of a coin at the moment.”